This invention relates to high voltage insulative shaft couplings, and in particular to an electrically insulative safety coupling which couples the two shaft members without positive mechanical interconnection and in a manner which will prevent high voltage electrical currents, i.e., voltages of on the order of up to about 50 kilovolts, from passing from one shaft member to the other. The coupler of this invention is particularly adapted to couple an underground moling auger or drill bit to the drilling machine, so that if a buried high voltage electrical cable is accidentally hit, the operator of the auger will be fully protected from electrical shock.
An earth moling operation can be quite dangerous if there is buried high voltage cable in the area. While precautions are taken to avoid hitting such a cable during the moling operation, the location of the buried cable might not always be accurately known or the operator may unwittingly aim his moler in a direction of the high voltage cable. If the high voltage cable is hit, there is great danger of electrocution because such cables typically carry up to about 50 kilovolts of electricity.
Shaft couplers are well known. For example, U.S. Pat. No. 4,348,672 discloses a coupler having driven and driving members separated by a dielectric material. The material is held in place and the driven and driving members are interconnected by a positive mechanical connection, set forth in several embodiments of this patent.
Other patents disclose other forms of couplers which, again, form positive mechanical interconnection between a driven portion and the driving portion of the coupler. Further examples are U.S. Pat. Nos. 3,402,572 (utilizing an adhesive), 2,449,654 (using fasteners to connect to an intermediate pad), 3,306,078 (using an undulating configuration to mechanically interconnect shaft portions), and 939,829 (utilizing a flexible disk having lugs which interengage the driving and driven shafts). Whenever a positive mechanical interconnection is provided, normally costs of formation of the elements and assembly of the shaft coupler are increased.
Of even greater importance, the devices of the prior art are incapable of preventing the passage of high voltage electrical current and of preventing electric shock should the driven auger accidentally hit a buried high voltage electrical cable. Even if the auger should hit an obsticle it may slip in rotation but the metallic parts will never come into contact. Thus the mechanism is fail-safe against metal-to-metal contact and electrical continuity.